Electric discharge apparatus



Nov. 11, 1941. w:E, BEKEY 2,262,381

ELECTRIC DISCHARGE APPARATUS Originzil Filed Sept. 29, 1936 Patented Nov. 11, 1941 2,262,381 OFFICE I ELEc'rRIo DISCHARGE APPARATUS William E. Bel-key, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Comgh, Pa., a corporation of pany, East Pittsbur Pennsylvania Original application September 29, 1936, Serial No. 103,185. Divided and this application January 10, 1940, Serial No. 313,239

3 Claims.

My invention relates to electric discharge apparatus and it has particular relation to discharge apparatus for signalling purposes.

This application is a division of application Serial No. 103,185, filed September 29, 1936 now Patent No. 2,201,003. i

Various systems have heretofore been used for producing and transmitting light signals. In one of the most widely used signalling systems a handcontrolled shutter or a rotating disc is moved in the path of a beam of light. The efliciency of such an arrangement is low since it requires that the light be operated at full brilliancy all of the time.

Other prior artsystems of which I am aware have similar efilciency limitations or are complicated in structure ,and diflicult to operate.

It is accordingly anobject of my invention to starting current through the starting electrode will be substantially decreased.

The novel features that I believe to be characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with further objects and advantages thereof, will best be underprovide signalling apparatus of simple and inexpensive structure that shall operate efficiently.

Another object of my invention is toprovide a source for signalling purposes'that shall be capablelof emitting radiations of high intensity and substantially without thermal inertia together with a circuit to control the source.

An incidental object of my invention is to provide a simple and inexpensive electric discharge device particularlyadapted to signalling purposes.

An ancillary object of my invention is to provide a sourcewhich may be used for photography of fast moving objects or. for conversion of li ht impulses into electric impulsesin conjunction with a photo-cell. A

In accordance with my invention I provide an electric discharge device for signalling purposes which comprises an evacuated vessel having disposed therein at least one electrode composed preferably of mercury or other metal capable of emitting electrons when excited. A collecting electrode which cooperates with the emitting electrode is disposed in the vessel .and an igniting electrode composed of boron carbide, silicon Ca bide or otherresistantmate-rial is supported from the collecting electrode and is in contact with the emitting electrode. When a current is transmitted through the starting electrode and the emitting electrode, .a discharge is initiated and a comparatively heavycurrent is transmitted between the emitting electrode and the collecting electrode. i

The type of discharge devices as the oneto which this invention is particularly applicable is generally known as. .ignitron, described in United States Patent .No..2,06.9,283, issued Eebrur ary 2, 1937.

Sincethe starting electrode is composed of material having a higher resistivity as compared to the effective resistance of the arc path, the arc will bridge the starting electrode and the flow of stood by *reference to the following description taken in connection with the accompanying drawing, in which:

Figure 1 is a sectional View showing a discharge device constructed according to my invention; 1

Fig. 2 is a diagrammatic view showing an embodiment of my invention;

Fig. 3 is a diagrammatic view showing a modification of my invention; and

Fig. 4 is a diagrammatic view showing another modification of my invention.

Fig. 5 is apartial diagrammatic view illustrating the use of a grid-controlled tube.

The apparatus shown in Fig. 1 comprises an evacuated envelope I provided with a plurality of lead-in wires 3and 5. The'envelope ,I may be constructed of glass or quartz or other transparent material, or it maybe constructed of metal having a transparent opening or window. One of the lead-in wires 3 is threaded at .the end 4 that projects into the envelope I.

A disc I having the form of a spherical sector and provided with an opening at its center is slipped over the threaded end 4 of the wire 3. The disc "I operates as an anode. One end of the starting electrode 9 is placed in direct contact with anode 1 by fastening it over the threaded end of the lead-in wire 3. The other end of the starting electrode 9 is in contact with a pool of mercury II which functions as a cathode.

The starting electrode 9 is ordinarily a bar of boron carbide, although other resistant material such as silicon carbide may be used. The pool of mercury which comprises the cathode ll may be replaced by asolid metal such as tin. Mercury, however, has an advantage as cathode material in that the metal vaporized by the discharge will run back down the walls of the envelope 1. The lower end of thestarting electrode 9 is coated with some insulating material l3 such as silica paint or glass. When a current of predetermined magnitude flows through the starting electrode 9 to the cathode, an arc is initiated. To confine the arc to a certain spot, a portion of the lower end of thestarting electrode 9 is left uncoated.

. Hereafter, I shall use the expression cathode (or electrode) of .the mercury type meaning or igniting electrode meaning thereby a bar of boron carbide or any material of high resistivity such as silicon carbide which may be utilized for the purpose of my invention. It is to be further understood that when the expression high resistivity is used, it means that th resistance of the material composing the starting electrode 9 is high relative to the effective resistance of the arc path.

In the apparatus shown in Figure 2, a capacitor I5 is provided and it is charged by a suitable source of potential indicated by way of example by battery I6. In series with the battery I6 is a variable resistor II which limits the charging current and hence determines the time which it takes the capacitor I5 to charge to full voltage. Thus, for a given supply voltage, the time it takes for the capacitor I5 to reach 63% of the battery voltage is expressed mathematically by the following equation t=RC where R is the current limiting resistance I! and C is the capacity of the capacitor I5.

The upper plate of the capacitor I5 is connected to one terminal of a switch I9 which is in the usual practice of my invention a telegraph key, although a grid-controlled tube 5| as shown in Fig. 5 may be used. The key I9 when depressed, connects the upper plate of the capacitor I5 to the discharge device I. The current then flows through lead-in wire 3 to the anode cap 1, passes through the starting electrode 9 which is in contact with the anode I to the cathode II. The current may be of the order of several thousand amperes and persisting for only a few micro-seconds produces a discharge at the junction of the starting electrode 9 and the cathode surface II.

Th capacitor I5 may be an electrolytic condenser with capacity ranging from 1 to 100 microfarads. The inductance 2| and resistance 23 together with the capacitor I5 determine the discharge character. In many cases Where a very short time light impulse is desired, the resistance 23 and inductance 2| may be only the circuit lead resistance and distributed inductance inherent in the leads. The current producing the discharge determines the amount of light emitted by the lamp. Thus, for a very intense light, a discharge of several thousand amperes for a few micro-seconds may be used. For a practical case, the arc drop may be 20 volts or less, the starting voltage 50 volts, the capacitor or battery voltage 100 volts or more. When the arc bridges the starting electrode 9, as heretofore described, the surge impedance of the circuit may be .05 ohm or less permitting a flow of several thousand amperes for a few micro-seconds.

The illumination from the are formed may be confined to one spot by shielding the starting electrode 9 over all but the desired spot. By the aid of a suitable lens 25 and reflector 21, the light from the cathode spot may be reflected, condensed or otherwise directed to form a large or small or concentrated or diverged beam of light. The light may be of a single pulse persisting for only a fraction of a micro-second, or it may be of an oscillatory nature with repeating flashes. By repeating the condenser discharges so as to produce 30 or more light flashes per second, the light signals may be made to appear steady. Any known standard type of receiving apparatus 28, for example a photocell, may be used to pick up the light flashes through an amplifier 29 and then transformed to impulses of an electrical nature.

While the circuit above described by virtue of the particular tube structure according to this invention presents an extremely compact arrangement, one must bear in mind that other circuits may be used with an equal degree of satisfaction. Fig. 3 of the drawing shows one modification of my invention using an ignitron tube 3| such as described in the United States patent previously referred to. It is to be noted that the starting electrode 33 must necessarily be connected outside the vessel through suitable circuit elements to the anode 35. Therefore, a resistor 31 is inserted in series with the starting electrode 33 to limit the discharge current. When the key I9 is closed, current flows from the positive side of the condenser I5 through the igniting electrode 33 to the cathode II, and to the negative terminal. The sum of the starting electrode resistance and the resistance 31 must be low enough to permit the flow of sufficient current to create a cathode spot and thereby start the tube. The remainder of the circuit and mode of operation is substantially the same as in the previously described circuit.

The circuit shown in Fig. 4 may be utilized when an alternating source of current is used. Power is supplied from a suitable transformer 4| and a rectifier 43 converts the alternating current into direct current which flows to the lead-in wire 3 thence to the discharge device which is constructed according to my invention. The discharge device I also acts as a rectifier and assists in the rectification of the current.

While I have illustrated but one form of device for carrying my invention into effect, and have indicated in a diagrammatic way several circuit connections for utilizing my invention, it will be apparent to those skilled in the art that my invention is by no means limited to the particular device or circuit arrangements shown, but that many modifications in the form of the apparatus used, as well as in the circuit arrangements employed, may be made without departing from the scope of my invention.

I claim as my invention:

1. An electric discharge device comprising a cathode composed of a material capable of emitting electrons, an electrode mounted to cooperate with said cathode and an igniting electrode in electrical contact with both said cathode and the first-named electrode and supported by said first-named electrode.

2. An electrical discharge device comprising an envelope, a cathode composed of material capable of emitting lectrons, an anode mounted to cooperate with said cathode, and a bar of high resistant material having an insulating coating on a substantial portion of the surface thereof, supported by said anode and in electrical contact with both said electrodes.

3. An electrical discharge device comprising an envelope, a cathode of the mercury type, an anode, and a bar of silicon carbide composition having an insulating coating on a substantial portion of the surface thereof, supported by said anode in such manner that it contacts electrically said cathode and said anode.

WILLIAM E. BERKEY. 

